Swinden Quarry — Rock Face Stabilisation

Griffiths were engaged by Tarmac in July 2020 to review a preliminary design to install rock fall protection mesh above several haul roads in Swinden Quarry North Yorkshire.

Rope Access Technicians drilling Rope Access Technicians drilling and installing (FRP) fibre re-enforced plastic bolts
swinden quarry Rock face stabilisation at Swinden Quarry

The preliminary design required rock fall mesh to prevent localized toppling of large blocks and fragments of rock from the crest and faces of the existing pre-split blasted benches.

The main purpose of the works being the safety for staff and heavy plant whilst reclaiming an extensive volume of material from the quarry crest into the quarry basin to allow further production of material in new areas over a 10-year period.

The works consisted of two distinct areas requiring intervention.

Face sections 29 to 41- Upper Face:

10,000m² of Deltax rock netting covering two separate benches measuring 330m in length each requiring top and bottom cables secured to 250No galvanised rock bolts 2m in length.

In addition, an existing cave feature at the toe of the lower face covering an area of approximately 100m2 required 100mm thick fibre reinforced sprayed concrete applied to spot bolts

Face sections 55-64 Lower Face:

15,000m² of Deltax to cover three benches measuring 170m in length requiring top and bottom cables secured to 150No galvanised rock bolts 2m in length.

Griffiths Operational leads and Geotechnical Engineers met with key stakeholders at the quarry to understand requirements of the workscope including access, safety, material specification and cost. Overcoming the challenges to deliver the works safely in a hazardous environment were not straight forward. Mitigating rock fall whilst installing rock bolts above busy haul roads, plant and workforce interface, access to the quarry crest, and future delays for quarry production if steel anchors could not be retrieved post blasting before entering large rock crushers.

Rope access technicians de-scaling rock faces. Rope access technicians de-scaling rock faces.
Installation of FRP rock bolts using lightweight drill. Installation of FRP rock bolts using lightweight drill.
Installation of FRP rock bolts using lightweight drill. Installation of FRP rock bolts using lightweight drill.

Safety for our workforce being our main priority, Griffiths challenged the design and sequence of works by reviewing the client’s delivery programme for future works to ensure obligations were met whilst eliminating risk for the client and contractor.

Traditionally, rock bolts are installed ahead of installing protection mesh. Our in-house rope access technicians worked from the quarry crest to toe, de-scaling sections of the pre-split benches removing all loose material prior to installing crest anchors and dropping mesh ahead of bolt installation. Using a spreader tool to enlarge the small apertures in the mesh, allowed our technicians to drill holes into the rock without damaging the protective coating on the mesh. By reversing traditional methods, Griffiths implemented control measures to de-risk rock fall, ensuring the safety of our workforce and plant using quarry haul roads.

Working with our supply chain ahead of the planned delivery programme Griffiths developed 2No unique light weight drilling frames complete with CP69 drills attached to eliminate the need to use excavators with drilling attachments, thus alleviating the use of haul roads and working during unsociable hours.

The drills could be operated by our in-house rope access technicians on the 80m high rock faces without the need for extensive temporary works designs and more importantly eliminating HAVS for our workforce.

Our in-house geotechnical engineers reviewed the use of galvanised rock bolts and the risk posed during processing quarried material. Fibre re-enforced bolts were proposed and accepted as an alternative method therefore totally eliminating future risk. Additionally, reducing the weight of each bolt decreased the manual handling impact for our workforce therefore minimising fatigue issues.

Tecco G65/4 rock fall mesh installed over existing cave Tecco G65/4 rock fall mesh installed over existing cave.

To mitigate the need to spray concrete around the existing cave, our design engineers proposed using G65/4 TECCO mesh with additional spot bolts. The proposal was accepted, therefore removing the need to block the adjacent haul road with large MEWPS, thus preventing delays for quarry production.

All works were completed in collaboration with Tarmac, 1-week ahead of our delivery programme, within the initial budget, without any defects, and most importantly, without any accident or incidents.

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